1. Field of Invention
The present invention relates to a fan and a blade thereof, and more particularly to a fan and a blade thereof with a better airflow efficiency.
2. Related Art
As shown in FIG. 1, a conventional fan 1 includes a frame 11 and an impeller 12. The frame 11 has a shell 111 and a base 112. A plurality of ribs 113 are connected between the shell 111 and the base 112. Moreover, a motor (not shown) may be disposed in the base 112. The impeller 12 has a hub 121 and a plurality of blades 122 disposed around the hub 121. The impeller 12 is disposed in the base 112 of the frame 11 via the hub 121 and is driven by the motor to rotate with respect to the base 112. Therefore, each blade 122 enforces nearby air to produce airflow.
As shown in FIG. 2, the connection line between the leading edge L and the trail edge T of each blade 122 forms an installation-angle β with the bottom surface of the impeller 12. The angle between the connection line and the airflow direction into each blade 122 (as indicated by the arrow) is defined as an attack-angle α°
In practice, the angle of the airflow entering the fan 1 changes with respect to the rotating speed of the fan 1, and then the attack-angle α is changed. Once the attack-angle α exceeds a critical angle, the airflow is separated from the surface of each blade 122, and a vortex is generated above each blade 122. In this situation, the airflow cannot be further increased even if the rotating speed of the fan 1 is raised. This is the so-called stalling phenomenon. Not only the airflow efficiency of the fan 1 cannot be enhanced, it also produces noises to waste the energy consumption of the fan 1 and the airflow efficiency is thus reduced.
It is thus imperative to provide a fan and a blade thereof to solve the above-mentioned problems.